Conventionally, there has been proposed a method of providing gas charges (gas rates, gas fees) corresponding to respective gas instruments to increase the sales of the gas instruments which use a gas as a fluid. For example, Patent Literature 1 discloses a method of calculating a discount charge corresponding to the usage amount of the gas for a gas instrument which consumes a great amount of the gas, such as a gas burner in a winter season.
So far, fuel cells have been put into practical use in large-scale or medium-scale power generation equipment. In recent years, fuel cells for household use have been developed, and have been available in the market. Hydrogen is required to generate electric power in the fuel cells. In the fuel cells for household use, a hydrocarbon based gas (city gas or liquefied petroleum gas (LP gas), etc.) supplied for home is used as a hydrogen supply source. Therefore, the fuel cells for household use can be deemed as “gas instrument”, because of the use of the gas. To achieve energy savings in a society in recent years, various charge menus for the fuel cells have been proposed. For example, Patent Literature 2 discloses a fuel cell system which decides the gas charge based on a plurality of payment structures corresponding to utilization (gas consumption amount, power generation amount, exhaust heat amount) of the fuel cell.